1. Field of the Invention
The present invention relates to carbon-carbon composites, and more particularly to composites made from fibrous carbon material, a thermosetting resin and a boron containing compound.
2. History of the Prior Art
It is known to use boron in the manufacture of carbon material such as graphite made from a filler such as graphite powder and graphitizable material such as pitch or a resin. The boron enhances the combination of the materials and the conversion thereof into graphite.
It is also known in the art to use boron in the manufacture of carbon-carbon composites comprised of fibrous carbon material such as carbon or graphite cloth and a thermosetting resin. Examples of this type of composite are provided by U.S. Pat. No. 3,672,936, issued June 27, 1972 to Leo C. Ehrenreich. The Ehrenreich patent recognizes that there is some improvement in interlaminar tensile strength as well as in oxidation resistance when a boron containing compound is added to the resin impregnated fibrous carbon material prior to carbonization of the resin.
However, what the prior art has failed to recognize is that the interlaminar tensile strength of laminated carbon-carbon composites is greatly improved with use of boron, particularly amorphous boron, if the composite is heated to a temperature of at least about 2150.degree. C. during carbonization and graphitization thereof. Thus, while the Ehrenreich patent suggests use of temperatures as high as 2800.degree. C., the examples set forth therein use temperatures well below 2150.degree. C. At temperatures below 2150.degree. C. the voids formed within the resin during decomposition thereof fail to knit properly despite the presence of boron, leaving the finished composite with relatively low interlaminar tensile strength. The prior art has also failed to recognize that while interlaminar tensile strength may be greatly improved with temperatures at or in excess of about 2150.degree. C., the tensile strength in the directions of the fibers of the fibrous carbon material is seriously degraded.
Accordingly, it would be desirable to provide carbon-carbon composites having greatly improved interlaminar tensile strength.
It would furthermore be desirable to provide carbon-carbon composites having both improved interlaminar tensile strength and substantial tensile strength in the directions of the fibers of the fibrous carbon material.
It would furthermore be desirable to be able to use boron and boron containing compounds in the presence of fibrous carbon materials at high temperatures without adverse effect on the fibrous materials.